The present invention can be considered as actually, if not legally, a division of my copending application entitled "Arithmetic Unit for a Postage Meter", filed on even date herewith, U.S. Pat. No. 3,890,491 issued June 17, 1975, and as such, is complementary to the mechanisms described in my copending applications entitled "Register for a Postage Meter", filed on even date herewith, U.S. Pat. No. 3,876,870, issued Apr. 8, 1975; "Print Head for a Postage Meter", also filed on even date herewith, U.S. Pat. No. 3,918,361, issued Nov. 11, 1975; and "Lock for Selection Mechanisms for a Postage Meter", filed on even date herewith, U.S. Pat. No. 3,892,355, issued July 1, 1975.
Postage meters are made under strict regulations prescribed by the U.S. Post Office which require, among other things, that a value selected for the meter must be accurately set in the value printing stamp of the meter and accurately set into each of two registers: one in which the values are accumulated known as the "ascending register", and one in which a value of the stamp is subtracted from the value set by the Post Office at the time of payment for postage, known as the "descending register"; and a mechanism which locks the meter against operation when the value in the descending register falls below that which could be set into the meter by the operator. The particular mechanism described and claimed herein relates to the selection mechanism for such a postage meter. For purposes of exemplification only, one order of the selection mechanism will be described, although it will be understood, as explained hereafter in the specification, that there will be a plurality of such mechanisms, one for each order of the registers, into which values may be set and a print head in which it is desired to select a value to be registered and printed. It is well-known in the art that the Post Office with which a meter is registered will, upon the payment of an amount to cover postage desired by the user, reset the descending register from time to time, but the values accumulated in the ascending register are never changed except by machine operation.
Other requirements of the Post Office are that the meter must be accurate in all aspects of its operation. It should be ruggedly constructed to withstand long and hard usage and it must be relatively trouble-free. It is well-known that a meter is so encased in its cover that it cannot even be repaired and the mechanism cannot be changed in any way except to change what are known as "slogan" dies on the print head and except that the descending register can have its setting changed at the Post Office when a Post Office official unlocks access to that register -- any other repair or change in the meter requires that the meter be officially taken out of service by the distributor and repaired in a facility that is subject to Post Office inspection. Hence, it is essential for a satisfactory postage meter to be rugged and trouble-free in its operation.